1. Field of the Invention
The present invention relates generally to a character recognition preprocessing method and apparatus, and more particularly to a preprocessing method and apparatus for improving the accuracy of character recognition for a character string including a nonlinear distortion.
2. Description of the Related Art
In a vision-based system, various information recognizable by a human being is generally included in an image acquired from a camera. Characters are very important object information through which information can be processed and transmitted most efficiently and accurately in a vision-based system. Research on such object information has increased as applicability for character information has risen and diversity has been required for contents with the development of systems and technologies. In particular, characters included in a natural image provide a detailed representation of implicative information on a surrounding environment. Therefore, research on intelligent visual perception vision systems for character extraction, recognition, and application is being pursued in various fields.
For example, such research is underway in an intelligent visual perception robot system, a guide system for the disabled, and a conversion system between different languages for travelers. Research is also being conducted to provide diverse contents in handheld devices with a camera mounted therein, that is, mobile systems such as a cellular phone, a Personal Data Assistant (PDA), and a smart phone. Most existing technologies concern fields of character detection and extraction, binarization, and recognition, and a character recognition and conversion system for the disabled by use of a mobile system is also being studied.
In a typical natural image, a change in shade may be caused by sunlight even in regions having the same characteristic and color, and this effect results in difficulty in the understanding of a natural image. In order to solve this problem, a character region is separated from a background in an efficient manner by performing a recovery process through non-uniform illumination correction and color correction. Further, a problem of the tilting of a character region according to photographing positions of a camera is solved by linear affine conversion.
In this manner, since character information appearing in a natural image has various types of distortions, as well as various types of sizes, colors, fonts, and directions, many problems must be solved by a preprocessing procedure for character recognition.
In particular, when an image is acquired from a curved subject where characters exist, such as a label of a bottle, a distortion occurs in which the size of a character object nonlinearly decreases with an increase in the distance from the center of the image. Such a distortion increases algorithmic complexity in analyzing an image, and causes performance deterioration in a recognition system. Further, even with characters arranged in a flat plane, the performance deterioration may be caused in the process of character recognition when the characters are arranged in a curved form.
Further, such a distortion is highly likely to obscure information on the inherent meanings of characters and cause false recognition of the characters. Therefore, there is a need to remove the non-uniformity of nonlinear characters and correct a distortion by using the structural characteristics of neighboring characters.